Optical materials and optical products are useful to control the flow and intensity of light. Examples of useful optical products include optical lenses such as Fresnel lenses, optical light fibers, light tubes, optical films including totally internal reflecting films, retroreflective sheeting, and microreplicated products such as brightness enhancement films and security products. Examples of some of these products are described in U.S. Pat. Nos. 4,542,449, 5,175,030, 5,591,527, 5,394,255, among others.
Optical products can be prepared from high index of refraction materials, including monomers such as high index of refraction (meth)acrylate monomers, halogenated monomers, etc., and other such high index of refraction monomers that are known in the optical product art. See, e.g., U.S. Pat. Nos. 4,568,445, 4,721,377, 4,812,032, and 5,424,339. The monomers can be cured or polymerized to take the form of a product capable of modifying or controlling the flow of light. In the particular structure of a microreplicated optical product, the monomers can be polymerized into a brightness enhancement film having a microfine prismatic pattern. See U.S. Pat. Nos. 5,175,030 and 5,183,597. Brightness enhancement films (BEFs) are very useful in many of today's electronic products to increase the brightness of a backlit flat panel display such as a liquid crystal display (LCD) including those used in electroluminescent panels, laptop computer displays, word processors, desktop monitors, televisions, videocameras, and automotive and avionic displays.
Monomers used to prepare high index of refraction materials desirably exhibit very specific optical and physical properties. One important property of such monomers is a high index of refraction, because this property allows the monomer, or polymers thereof, to effectively control the flow of light. Additionally, such monomers preferably are soluble in other monomers, or can readily dissolve other monomers; that is, particularly preferred high index of refraction monomers can act as solvents to dissolve other monomers, allowing the mixture of monomers to exist in a liquid composition. Finally, preferred monomers or high index of refraction polymerizable compositions and polymers exhibit the ability to adhere to materials used as other components (e.g., substrates) within an optical product. There exists a continuing need for high index of refraction monomers that can act as a solvent, and that adhere well to other materials.
With respect specifically to brightness enhancement films, the index of refraction of components of a BEF is related to the brightness gain or "gain" produced by the brightness enhancement film. Gain is a measure of the improvement in brightness of a display due to the brightness enhancement film, and is related to the index of refraction of the material used to prepare the film, as well as the structure (i.e., geometry) of the brightness enhancing portion of the film. A high gain is desired for a brightness enhancement film because improved gain provides an effective increase in the brightness of a backlit display. Improved brightness means that the electronic product can operate more efficiently by using less power to light the display, thereby reducing power consumption, placing a lower heat load on components of the display, and extending the lifetime of the product. Thus, because of these advantages, there exists a continuing need to find optical products to provide improved levels of brightness gain, with even very small, seemingly incremental improvements being quite significant.